1. Field of the Invention
The present invention relates to a control apparatus for controlling an output voltage of a power conversion apparatus with a chopper circuit including voltage-controlled type switching elements and a coil to generate back electromotive force, and relates to a power conversion system including the control apparatus and the power conversion apparatus.
2. Description of Related Art
It is known to on/off-control switching elements of an inverter in accordance with results of comparison between a command voltage to an electric rotating machine and a carrier signal, so that the electric rotating machine is applied with a voltage having a step-like sinusoidal waveform at each input terminal thereof. However, since the output voltage of the inverter varies in a step-like manner, there occurs a problem that the neutral-point voltage of the motor varies by a large amount as a result of which common mode noise and a large surge voltage appear.
To cope with such a problem, it is known to provide a DC/DC converter with a capacitor in which a converted voltage to be supplied to one of the three phases of a three-phase electric rotating machine is accumulated as shown in FIG. 19. For more detail, refer to Japanese Patent Application Laid-open No. 2006-136125. In this case, since the three-phase electric rotating machine is applied with a voltage having a smooth sinusoidal waveform, it is possible to suppress the surge voltage.
Meanwhile, when such a DC/DC converter is used so as to pass a current between the DC/DC converter and an electric rotating machine, it is necessary to rapidly change the voltage accumulated in the capacitor thereof. In this case, since a switching frequency of the switching elements becomes high, the switching elements are required to have a switching speed sufficiently fast in order to keep control response of the output voltage sufficiently fast.
However, the inventors of the present application have found that the switching elements having such a high switching speed tend to generate noise exceeding the withstand voltage between a conduction control terminal and an output terminal thereof.